The present invention relates generally to the treatment of subterranean formations with crosslinked treatment fluids, and more particularly to treatment fluids that comprise a zirconium isopropylamine crosslinking agent and associated methods.
A variety of subterranean treatments using crosslinked treatment fluids have been developed. One subterranean treatment that uses a crosslinked treatment fluid for stimulating production from a subterranean formation is a fracturing treatment. Fracturing treatments generally involve pumping a crosslinked treatment fluid (e.g., a fracturing fluid) into a subterranean formation at a pressure sufficient to create or enhance one or more fractures in the subterranean formation. The fracturing fluid generally has a viscosity that is sufficient to suspend proppant particulates and to place the proppant particulates in fractures, inter alia, to maintain the integrity of those fractures once the hydraulic pressure is released. Once at least one fracture is created and the proppant particulates are substantially in place, the viscosity of the fracturing fluid usually is reduced, and the fluid may be recovered from the formation. Other treatments that use crosslinked treatment fluids include, but are not limited to, sand control treatments (e.g., gravel packing), drilling operations, polymer floods, and forming temporary plugs or blocks in subterranean formations, and the like.
Crosslinked treatment fluids generally comprise an aqueous fluid and a crosslinked gelling agent, wherein the crosslinked gelling agent may be the reaction product of a reaction that comprises a gelling agent and a crosslinking agent. This reaction between the gelling agent and the crosslinking agent is commonly referred to as “crosslinking.” Preparation of these crosslinked treatment fluids typically involves combining the aqueous fluid with the gelling agent. An optional buffer also may be included to provide an appropriate pH for hydration of the gelling agent and crosslinking. Next, a crosslinking agent may added for crosslinking one or more gelling agent molecules. Generally, the crosslinking may occur very slowly and/or not at all while the treatment fluid is at or below ambient temperature. As used herein, “ambient temperature” refers to a moderate temperature range normally encountered on the surface. For instance, certain crosslinking agents, such as zirconium lactate, may require temperatures greater than about 85° F. to about 90° F. to initiate crosslinking.
After preparation, the treatment fluid may be placed into a subterranean formation through a well bore. Because most subterranean formations are relatively hot, e.g., having temperatures in the range of from about 100° F. to about 400° F., the treatment fluid may be heated as it passes through the well bore and into the subterranean formation. As the treatment fluid heats to temperatures greater than ambient temperatures, crosslinking may occur to form a crosslinked treatment fluid that may have a desired viscosity for a particular application (e.g., proppant transport). Treatment fluids, such as those described above, may be described as delayed crosslinking aqueous gels because crosslinking does not occur or occurs very slowly prior to introduction of the treatment fluid into the well bore. An example of a delayed crosslinking aqueous gel comprises an organic carboxylated gelling agent, an aqueous fluid, a buffer (capable of maintaining the pH of the fluid at about 5 or above), and a zirconium IV-containing crosslinking agent.
However, in some instances, the aqueous fluid used to form the gelled treatment fluids may be relatively cool (e.g., below about 70° F.) and may even have temperatures as low as about 35° F. Where these relatively cool aqueous fluids are used, the formation temperatures may not be sufficient to heat the gelled treatment fluids to temperatures suitable for crosslinking while the gelled treatment fluids are resident in the well bore. If these temperatures are not reached, the gelled treatment fluids may be introduced into the subterranean formation with little or no crosslinking, and thus the gelled treatment fluids may not have viscosities sufficient for the particular applications. This problem may be particularly apparent in relatively shallow wells where the time the gelled treatment fluid is resident in the well bore may be short when compared to deeper wells.